This invention relates in general to frame assemblies for vehicles. In particular, this invention relates to a joint structure between a closed channel structural member and an open channel structural member in such a vehicle frame assembly, and to a method of manufacturing such a joint structure.
Virtually all land vehicles in common use, such as automobiles and trucks, include a frame which serves as a platform upon which the remainder of the vehicle is built. Many vehicle frame structures are known in the art. Most of these known vehicle frame structures are formed from a number of individual metallic components which are permanently joined together. For example, one type of vehicle frame structure is known as a full perimeter frame assembly. A typical full perimeter frame assembly is composed of a pair of longitudinally extending side rails which are joined together at the front by a forward cross member, at the rear by a rearward cross member, and at intermediate locations by one or more intermediate or auxiliary cross members. The cross members not only connect the two side rails together, but also provide desirable lateral and torsional rigidity to the vehicle frame assembly. The full perimeter frame assembly functions as a platform upon which the body and remaining components of the vehicle are supported.
Each of the side rails of the vehicle frame assembly may be formed either as a single individual structural member or as a plurality of individual structural members which are secured together. In shorter length vehicles, each of the side rails is usually formed from a single integral side rail member which extends the desired length. In longer length vehicles, however, each of the side rails is usually formed from two or more individual side rail members which are permanently joined together, such as by welding, to provide a unitary side rail which extends the desired length. In either instance, it is known to form the side rail members from either open or closed channel structural members. Open channel structural members can be characterized as having a non-continuous cross sectional shape, such as C-shaped or hat-shaped channel members, for example. Such open channel structural members are relatively easy and inexpensive to shape into desired configurations and to secure together. Closed channel structural members can be characterized as having a continuous cross sectional shape, such as tubular or box-shaped channel members, for example. Closed channel structural members are desirable because they are generally stronger and provide better torsional stiffness than open channel structural members of comparable weight.
One manufacturing process which is being increasingly used to manufacture closed channel structural members, including those used as vehicle side rail members, is the process of expansion shaping, commonly referred to as hydroforming. Hydroforming is a well known process which uses pressurized fluid to deform a tubular member into a desired shape. To accomplish this, the tubular member is initially disposed between two die sections of a hydroforming apparatus which, when closed together, define a die cavity having a desired final shape. Although the die cavity is usually somewhat larger than the tubular member itself and non-circular in cross sectional shape, the closure of the two die sections may, in some instances, cause some mechanical deformation of the tubular member. Thereafter, the tubular member is filled with a pressurized fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid is increased to a magnitude where the tubular member is expanded outwardly into conformance with the die cavity. As a result, the tubular member is deformed into the desired final shape.
In a typical hydroforming apparatus, the ends of the tubular member extend outwardly from the die sections during the hydroforming process to facilitate the connection of sealing heads thereto. The sealing heads are provided to seal the interior of the tubular member to permit it to be filled with a pressurized fluid. One or both of the sealing heads is connected to a source of pressurized fluid for filling the tubular member with fluid and pressurizing such fluid to expand the portion of the tubular member contained between the die sections outwardly into conformance with the die cavity. As a result, the ends of the tubular member which extend outwardly from the die sections are not deformed during the hydroforming process and, therefore, are generally maintained in their original tubular shape. Thus, the hydroforming process results in a closed channel structural member having a non-circular cross sectional shape (box-shaped, for example) throughout most of its length, but includes end portions having a circular cross sectional shape.
As discussed above, it is desirable in some instances to form the side rail from two or more individual side rail members which are permanently joined together. In some instances, a first side rail member may terminate in an end portion having a closed channel cross sectional shape, while a second side rail member may terminate in an end portion having an open channel cross sectional shape. For example, if the first side rail member is formed by the above-described hydroforming process, the end portion thereof will normally have a circular cross sectional shape, while the second side rail member will normally have a rectilinear cross sectional shape. In the past, the circular cross section end portion of the first side rail member was removed in a trimming operation to facilitate the connection of the second side rail member (referred to herein as an extension member) thereto. The trimming operation provided mating end portions on the first and second side rail members which were complementary in shape (i.e., both rectilinear in cross sectional shape), thereby facilitating securement by welding or other means. Although effective, the trimming operation increased the cost of the vehicle frame assembly by increasing manufacturing operations and time, while creating undesirable scrap. Thus, it would be desirable to provide an improved method of joining a first closed channel side rail member with a second open channel side rail member which eliminates the need for such a trimming operation.
Additionally, it has been found that known welding processes for securing the closed channel side rail member to the open channel side rail member involve the use of relatively intricate welds on several mating surfaces. These mating surfaces include both interior and exterior surfaces of the two side rail members, making the welding process relatively difficult to perform quickly and efficiently. Thus, it would also be desirable to provide an improve method of joining a first closed channel side rail member to a second open channel side rail member by means of relatively quick and simple welding procedures.